The present invention generally relates to electrochemical cells and, more particularly to electrochemical cells having current path interruption at high internal pressure.
Electrochemical cells or batteries are commonly used for portable, electrically powered devices. Many devices, such as laptop and handheld computers, portable communications equipment and the like, can put a heavy drain on the cells and batteries used to power them, and those cells/batteries must be capable of delivering adequate power at those high rates. Cells and batteries of certain electrochemical systems and/or designs are better suited for such high rate applications. Included among these are primary and secondary nonaqueous electrolyte systems having negative electrodes based on alkali metals (such as lithium and sodium) and either solid or liquid active positive materials, secondary aqueous electrolyte cells with nickel-based negative electrodes and positive electrodes containing active materials such as cadmium and metal hydrides, and primary and secondary aqueous electrolyte cells having zinc-based negative electrodes and manganese dioxide-based positive electrodes. Galvanic cells are hermetically sealed in a case to prevent loss of electrolyte by leakage. However, under certain conditions, the internal pressure of the cell can increase. For example, increased pressure can be caused by overcharging, overheating, reverse charging, or other abusive conditions. If the cell is permanently sealed, the buildup of internal pressure within the cell could cause the cell container to leak, bulge, or even rupture.
A number of approaches have been considered for preventing or reducing high pressure buildup in a cell due to an abusive condition. One approach is disclosed in U.S. Pat. No. 4,931,368, entitled "Vent Liner and Cover Construction for Galvanic Cells." According to the aforementioned U.S. patent, a vent liner is disposed within a sealing well and a seal member is force-fitted within the vent liner. The vent liner and seal are assembled such that the seal member is at least partially expelled from the vent orifice at a predetermined internal pressure within the cell. This allows for release of the high-pressure fluid from within the cell.
Despite the activation of a venting mechanism during a high-pressure condition, electrical current may continue to flow through the current path of the cell. This can lead to continued charging or discharging of the battery which may generate additional heat and may result in instability of the cell.